Table of Contents - The Atmospheric Studies Group at TRC

Section 2: Geophysical Data Processors
The GTOPO30 data set is divided into files (or tiles), where each file covers 40 degrees of longitude and
50 degrees of latitude, except for in the Antarctica region where each file covers 60 degrees of longitude
and 30 degrees of latitude.
Figure 2-2 shows the spatial coverage of the data files. Each file is either 57,600,000 (non-Antarctica) or
51,840,000 bytes (Antarctica) in size. These DEM data are provided in 16-bit signed integers in a simple
binary raster, with no imbedded header or trailer bytes and no internal indexing. The data are stored in
Motorola byte order, which stores the most significant byte first, i.e., big endian. The Motorola, SUN,
HP, and SGI platforms use big endian; whereas the Intel (PC) and DEC platforms use little endian.
Therefore, the user must be careful regarding the intended platform for TERREL. The code uses a logical
flag, LBIGENDIAN (set in subroutine SETGLOB), to define whether the intended platform is big endian
or little endian. LBIGENDIAN=.FALSE. is for little endian, and LBIGENDIAN=.TRUE. is for big
endian. The flag enables the porting of TERREL across different machine platforms.
3. User control file (TERREL.INP): this input file specifies the filenames and type of databases being
processed and the modeling domain related parameters. The format of the TERREL control input file
follows the same rules as those used in the CALMET.INP file (refer to the CALMET section for
details). Only data within the delimiter characters (!) are processed. The input data consist of a
leading delimiter followed by the variable name, equals sign, input value or values, and a terminating
delimiter (e.g., !XX = 12.5!). A sample file is shown in Table 2-2 and a description of each input
variable is provided in Table 2-3. Detailed information on the input variables is included in the
default input file itself.
TERREL.INP may be created/edited directly using a conventional editor, or it may be created/edited
indirectly by means of the PC-based, Windows-compatible Graphical User Interface (GUI) developed
for the geophysical preprocessors (CALPro).
4. Save file: this input data file contains the binary results from an intermediate run of TERREL. It is
read as input to the current run.
TERREL OUTPUT:
1. List File: echoes the selected options, reports errors and provides a listing of the gridded terrain
elevations and the number of raw data points ('hits') used to compute the terrain elevation for each
grid cell (e.g., TERREL.LST).
2. Plot File: can be read directlyCALPro’s CALVIEW or by a contouring software package such as
SURFER (e.g., TERREL.GRD).
3. Save File: contains the intermediate binary output (e.g., TERREL.SAV).
2-6